Process of treating zinc ores



1933- N. c. CHRISTENSEN PROCESS OF TREATING ZINC ORES Filed March 18, 1931 6 Sheets-Sheet l 100 Percenf/ Ac d,

9 8 7 6 6 4 6 Z 1 3*3 NR NQ 1933- N. c. CHRISTENSEN 1,937,633

PROCESS OF TREATING ZINC ORES Filed March 18, 1931 6 Sheets-Sheet 2 o 10 10 5o a0 I00 I10 /30 I40 15a /60 /70 /50 m0 200 2/0 220 I50 2'40 250 260 27::

Temp C INVENTOR 29 2 fid'fm VoLu/ne Zn. 0

Dec. 5, 1933. N. c. CHRISTENSEN ,6 3

PROCESS OF TREATING ZINC ORES Filed March 18, 1931 6 Sheets-Sheet 3 110 150 C'erdz'yrams Zn per ccwsolution mJO Zfl1'0// fi O 10 Z0 v 40 5O 7O 8O 1 0 1Z0 11570 1406. e INVENTOR Vblume Z Z a precipitated sulphide which may be usm as such .Patenteol Dec. 1933 I V 1,931,633 7 raocisss or musician zinc oats Nifilfl c. cal-sea en, saulllalre (titty, Utah Application March to, rear. Serial No. 523,576

realms. (or. est-is) This invention relatesto processes for the rebe used in the description to cover these various covery of zinc from its ores. The invention typesof ores. relates primarily to the treatment of zinc sulphide, As described in my U. S. Patent 1,434,08i, if H ores for the recovery of zinc therefrom as metal finely ground zinc sulphide ores or concentrates 501 as zinc sulphide. The main object of the I are mixed with a large excess oi hot sulphuric so invention is to treat the raw sulphide ores by acid of a concentration of 60%; or higher the hydrometallurgical methods Without roasting the zinc is dissolved in the excess of hot acid as ores and to finally recover the zinc from them zinc sulphate and the sulphur is driven ch as either as a metal by electrolysis or as a pure H25, the reaction c'rocee' as indicated below:

. Y 65 or from which the metal may be recovered also ZnS+H2SO4=ZnsQ4+H2s I I v by electrolysis. It is also an object of the in- As noted in this patent, acids of concentration vention to recover the sulphur combined with less than 6.0% have some dissolving action upon. the zinc in the sulphide ores as His for use in most zinc sulphide ores but a practically com-'- precipitating the zinc as 210.8 (or for other uses) plete extraction or the zinc is possible only with "m or for the recovery of elemental sulphur thereacids of a concentration of 60% or higher. For irorn. the treatment or" the sulphide ores or" eirample, in the treatment of a typical zinc-lead zinc by this invention a smaller proportion of sulphide ore from Pioche,Nevada, treatment with oxidised or carbonate ore of zinc is also treated hot l0% acid gave an extraction of only 32% 2 and it is also an object of the process to recover of the zinc, with acid an extractionoi-il57 75 the zinc from such ores. The chemical reagent with 60% acid an extraction of 95%,, with used in the recovery or the zinc iroxn these ores acid an extraction of 98%, and with %acid is sulphuric acid, used in suitable varying'con- 99%. As notedin the above patent the action centrations in the different steps of the process. of the hot acid upon the zinc sulphide and other.

25 It is an object of the invention to recover the constituents of the ore also varies with the cong0 H2804, used in decomposing the ores, (and discentration. Up to a-conc'entration of approxisolving the zinc out of the ores) either as such mately 70% the hot acid reacts with the 2x18 ror rurther use in theprocess or in other marketto form H23 but above this concentration sulphur able product. is-liberated-in increasing arnountstvith increase The invention is related to the processes disin acid concentration until with 95% acid subclosed in my I]. S. Patents 1,434,084, 1,415,?97, stantially all of the'sulphur is released as rne=- 1,435,699, in that it utilizes some of .the' clis tallic sulphur as indicated in the following coveries described in these patents. It aims, equation: however, to obviate certain defects and limits. l

35 tions of the older processes which militate against 3ZnS+fifsO4 3ZnSO+4H3-()+%S their practical use and also aims to recover the 'ilcids of a concentration up to oil% have little zinc in finished products other than zinc action upon galena except-to form a thin'supen sulphate. The invention accomplishes these purricial coating of PbSO with the more concern poses by a combination of new steps with some. trated acid. With increase in acid concentration oi the steps of these older processes and also in above 80% more of the lead is sulphated until 5 combination with other processes now in com with 80% acid the sulphating may be complete men use. By these combinations the invention veri, finely ground ores. Up to apprentsecures results which cannot be secured by znately 30% concentration the silver in the ore older processes and which are of great value and is not dissolved to any appreciable extentbut 45 importance in connection tv-iththe treatment or above this concentration is dissolves in increas- 10o zinc ores. The invention. is applicable to the ins." proportion'with increase in acid concentratreatment of all classes of zinc ores such as zinc tion. Only the very concentrated hot acids have sulphide ores and concentrates and the so-called any action upon pyrite or ohalcopyrite, even complex f or mixed lead-zinc sulphide ores and acid having no appreciable. action in the time 5Q concentrates. and is also applicable to the treat= of treatment required for the sulphatlon oi the merit of apronortion of oxidized or carbonate zinc. v r ores of zinc or mixed carbonate ores oizinc and As noted inU- SJ e 1, e Solubility lead in connection with the treatment of the or" ZnSOi in H2304 varies greatly with change sulphide ores. The terms sulphide ores oi inconcentration and temperature.' The appendainc and oxidized zinc ores will therefore ed curveairom U. .8. Patent 1,434,084show this variation insolubility. Fig. 1 consists of two curves,- A showing the solubility of ZnSOr in H2804 of varying concentration at the boiling point of the different acids; and B showing the solubility of ZnSOl in H2804 of varying concentration at '30 C. Fig. 2 consists of three; curves, A, B, and C showing the solubility of ZnSOr in'98%, 95%, and 80%- acids respectively at different temperatures.

Figure 3 consists of one curve showing the solubility of ZnSO in 60% H2504 at different temperatures. As also noted in this patent (US. Patent 1,434,084) to secure a substantially complete recovery of the I Zn from the sulphide ores by agitation in mix ture with the hot sulphuric acid it is necessary to use a sufl'icient excess of acid to dissolve the ZnSO4 which is formed. as otherwise. the Zn'is.

not sulphated and is not recovered either in the hot acid or in the subsequent water wash.- A

complete recovery of the zinc from'these ores therefore requires the use of a very large quantity of acid. For example, if 65% acid is used, this acid will hold 1.3% Zn in solution (as ZnSO4).

hot and .2% Zn cold, giving maximumavailable carrying power 1.1% Zn (as ZnSO-r). These fig-f ures represent volumetric percentages i. e. grams of zinc in 100 c. c. of acid. Ascom-plete saturation results in poor extraction, a practical carry- -ing power of the acid is one volume per cent zinc, i. e.', 1 gram of 'zinc per 100 c. c. of acid. Since the specific gravity of 65% acid is 1.56

' the; acid in'the mill circuit could dissolve only .64 grams of zinc per 100' grams of acid out of the ore as ZnSOr. The treatment of each ton of 1'9% ore would therefore require the handling of 30'tons of H2SO4 and the treatment of one ,ton of 58% zincsulphide concentrate would require the handling of over tons of acid. The

' gravity of ,the acids of higher concentration.

' In treating zinc sulphide, ores by the process of the above patent by agitating the'ores with the. hot sulphuric acid, I have'found, as noted;

above. that sufficient hot acid must be used to entirely dissolve the ZnSOr formed as otherwise a superficial coating of ZIISO4 is formed around the zinc sulphide particles which prevents entirely all' further action of the acid on the particle'. I have also found that if this zinc sulphate 'coating is continuously removed from the surface of the sulphide-particles,= during the treatment with the hot acid that the sulphating action continues until the zinc sulphide particles are allconver'ted to" ZnSOr; the sulphur being" i driven 011 as H28. as indicated in the following equationz' I have also found that 'this zinc sulphate coatingmaybe readily removed-by grinding .or attrition with small balls or pebbles during thetreatment withthe hot acid, making possible a complete. sulphating of the Zn'S in the ore by a-treatinent of from 15 to 30 minutes with only suflicient acid to make a thin pulp with the ore.

The ZnSOl thus formed remains as a solid mixed with the residual unattacked ore particles (silica.

- fully described below. The

pyrite, galena. etc.). To recover the zinc sulphate from this mixture the excess acid is firstremoved by filtration (for reuse in the treatment of more ore) and the ZnSO4 and residual acid are then removed by washing'with spent electrolytefrom an-electrolytic circuit-or with water to form an acid zinc sulphate solution.

-This acid zinc sulphate solution contains some iron, manganese and other impurities which may be removed as later described. v

, Inthistreatment of the zinc sulphide ores by grinding with hot H2804 I have also found that the sulphating effect varies with the acid concentration. Acids below 50% have little effect. With from 50% to'60% acid thesulphating increases rapidly, and for best results the acid concentration should be above 60% during the entire treatment, preferably 65%. Since the sulphatizing of the ZnS uses up acid and thereby, reduces the acid concentration, sufficient excess acid above 60% in concentration mustbe used so that theacid concentration does not fall below 60% (or preferably 65%) during the treatment, i. e., before all the ZnS- is sulphated. 1 1 I have also found that the sulphating action is efiicient and rapid only when the acid is near or atits boiling point and the treatment should therefore. be carried out with the acid held at or close to this temperature. The sulphating action of the hot acidduring the grinding varies with concentration, the stronger acids acting .more rapidly on the ZnS and sulphating any PbS in the ore to a somewhat greater extent than when the ore is not ground during treatment'with the acid. .Whether acids stronger than 65% are used in the treatment of mixed or-not it is desired to sulphlte the lead in the ore.- Acidsabove. 70% forms instead of. H28 in proportion to the increase in concentration and.

P bZn sulphide ores may depend upon whether cause aloss of acid and H23, and are therefore i not preferred over the acids of lower concentration for this'reasonas well as the greater difficul'ty of handling themore concentrated acid. The foregoing method of grinding the ZnS ore during treatment with the-hot acid makes possible the complete sulphation of the-zinc su lphide in these ores by.the use of a relatively f small amount of acid as compared with the older process mentioned above.' It also avoids the necessity of heating and cooling the acid used for. treating the ore to precipitate the ZnSOr therefrom; the ZnSO4 being formed and left in the ,sulphati-zed' product as a' solid and the hot excess acid filtered away from the solid ZnSOr and residue and this acid being reused in the treatment of more ore. Fromthe mixture of ZnSO and ore residue thus secured the'ZnSO4 maybe recovered by washingwiththe spent elec-'- trolyte-from an electrolytic circuit thus making possible .the'combination of this process with electrolytic processes for. the recovery' of the zinc in metallic form as described below. From the mixture of ore residue'and solid ZnSO4 secured in the process as above described. the.

ZnSO4 may also be dissolved ifpreferred, by

means ofwater to forma zinc sulphate solution from which the zinc may be recovered as ZnS, by means of the H28 made in the process, as more precipitated ZnS thus recovered may be used as a paint pigment.

or'for other similar purposes or may also be treated by electrolysis for the recovery of the zinc as metal as described below.

The application of the invention to ores of.

is a flow sheet of the process used in connec-,

tion with a high acid electrolyticv circuit. Fig. 6 is a flow sheet of the process as applied in con-- nection with the recovery of the zinc asa sulphide and the treatment of the sulphide by electrolysis for the recovery of the zinc as a metal;

Though the flow sheets illustrate a continuous operation, the-process may be carried out in batches. l

. The process of Fig. 4. is brief as follows: the ZnS,

the finely comminuted zinc sulphide ore or concentrate is first ground together with the hot sulphuric acid with small quartz pebbles (or other acid-proof material), in an acid-proof mill (or other suitable or attrition apparatus),

' called the sulphator (1); This device is kept hot by suitable jackets for the circulation of a suitable heating fluid. Thetime of treatment necessary to secure substantially complete sulphating of the Zns for most ores will vary from it) to minutes. With acids of the preferred concentration (between and 70%) the sulphur is driven on in this-treatment as H2S, which is utilized as later described. The hot mixture of excess acid, 211304 and ore residue from the sulphator v(1) goes to the filter (2) Where the excess acid is separated from the solids and returned through the heater and concentrator (3) to the head or? the circuit for use in treating more ore. The

I filter cake containing the-211304 and ore residue is next Washed free from ZnSOu and acid spent electrolyte and finally with Water preferably a counter-current washer l) or a washing system such as the standard arrangement of Dori 'thiclzeners, or the standard arrangement oi a series of filters for counter-current washing, or other suitaol washing device. Til the standard, or low acid,'electrolytic process, such as that in use at or Trail, is used, the spent electrolyte used for this Washing operation may contain in the neighborhood or ten per cent E2804 and 5% Zn. s solution is first used to dissolve all the 521150 thereafter th away from the As will he noted by reference to the l, a hot i hold over 2d% Zn as 21215564 so that ther no dificulty in (iissol-vinr, an amount of iivalent to that precipitated in the electrolytic circuit from the sulphated-ore in the spent electrolyte. acid zinc sulphate washes from ti counter current washer i) are preferably mixed and concentrated in a suitable evaporator or concentrator (5) until the con centration of the acid reaches approximately 69% (or slightly rm 2). As will be seen by reference to Fig. i, this restdts in the precipitation of near= ly all the This concentration is preferacly carried out three or more steps, the DPS.

each step so as to avoid the formation of an excessively thicls ZnSOr sludge toward the end of the concentrating operation. Thisstep is also preferably carried out in counter-current using the water evaporated from the acid 211E504 solution to dissolve the precipitated 211304 and thus contains some impurities such as iron, manganese,

esidue oi treated ore with water;

balance the heat of solution of the ZnSOr'in the water against the heat of concentration of the acid solution. The precipitated ZnSOr is filtered out of the concentrated acid on the 'filter '(6) and to form azinc sulphate solution. This solution cadmium, etc., dissolved out of the ore together with. the zinc. Toremove these impurities oxidized zinc ore is mixed with this acid'zinc sulphate solution in'the neutralizer- (8) to neutralizevthe acid. After the acid has been neutralized in the neutralizer (8),.sufiicient oxidizingagent (preferably PbOz) is addedto the mixture which is then agitated until the iron (and other oxidizable impurities)-- are precipitated. The residue of leached oxidized ore is then separated from the neutral zinc sulphate solution by filtration in the filter (9) and the zinc sulphate solution is treated with zinc (preferably zinc dust) toremove cadmium, copper, etc., in the precipitator (l0). l00

After separation of the precipitate in thefilter (11) the pure zinc sulphate solution is electrolyzed in the electrolytic cells (12). The spent electrolyte from these cells (12-) is again passed through the leaching circuit to take up its fresh i load of zincsulphate as described. If no oxidized ores or zinc calcines are available for neutralization of'the acid in the ZnSOr filter cake from the filter (6) or if it is not desired to-tre'at oxidized ores, this ZnSOi filter cake may be heated sumllll ciently todrlve off the H2604. leaving anhydrous 221604, which is then dissolved in water to make a neutral zinc sulphate solution. The oxidizable impurities such as iron, etc., are then precipitated from the solution by the addition. of an oxii solve more 2111804 outolmore sulphated ore.

The treatment of the leached residue from the counter current washer (4i) and filter (4a) will depend upon the character of the residue. If it 1125 contains lead it-rnay be treated by the brine leachingprocess described in my U. S. Paton; 1,539,711 for the recovery of the'lead and silver,

and the residue fromthis treatment may be treatedloy flotation to recover the pyr'i le which 13% carries the gold and residual silver in the ore.

the residue contains no lead it may betreated hyfiotaiion for the recovery, of the pyrite and gold and silver. J The treatment of the residueor" oxidized ore from the neutralizer d and filter, 9 vrill also vary with the character of the residue. 1 If it contains lead which after treatment will he present as lead sulphatathis may be recovered by leaching with brine, which may be slightly acidified so as to recover any silver in the ore. "1141 Figure 5 shows a modification oi the process as applied to recovery of the zinc by electrolysis in .ahhi' cipitated 21153 34. heing removed at the end of 1g ac d elec mlyte Such is used m the Tainton process. Aswillbe noted loyicomparing the flow sheets of Figs. deride, substantially the 5 only difference in the twocases is in the addition of part of the pure zincv sulphate-in solid form in successive cells of ihe electrolytic plant so as to lreep up the'zinc concentration in the electrol lyte as the acid concentration increases, and in 'w the use-"of. a higher acid concentration anda ' higher current density, and in the dissolving of gmsoi (orimore) and approximately 80 grams the-zinc sulphate out of the sulphated ore in a spent. electrolyte of much-higher acid concentration, and in the use of a much more concentrale'dneutral zinc sulphate solution entering the ..electrolytic-plant. The spent electrolyte from the electrolytic cell (12) in this case'may carry 300 (or morei-of'zn (as ZnSOQ; per litre. By reference to l'it will be seen that this solution can! carry between 14 and 15% Zn (as ZnS04); The spent electrolyte therefore able to take. 'up.

' an additional-'6%--7%' Zn in the counter-current 'w.asher .(4 the resldual'ZnSOr being washed out with water'in thefilter (4a) and counter-cur- :rent,w as'her (4).. In this case the ZnSO4 from the filter (6) isdissolved with just sufficient hot jwaier in thedissolver (7) and neutralized with the oxidized ore vin'the neutralizer (-8) soas .to

- form a hot approximately saturated ZnSO4 solutiong After treating thissolution with zinc-dust to. remove cadmium. copper, and other impurities,

this hotfconcentr'ated solution is cooled in ihe counter-current heat interchanger and crystalizer (13) thus precipitating out part of the Zn SOr as ZIISO4-6H2O and cooling the'solution before itsentrance to' the electrolytic circuit (12). .The precipitated ZnSO4-6H2O is added to the cell's near the end ofthe electrolyti-c"eircuit as indicated in the-flow sheet to maintain a sufilciently. high zinc concentration, as the acid builds up in .ihe circuit; to permit the use of a hlgh acid concentration and high current-density. If desired.

the ZnSO4-6Hz0 may preferably be heated in a suitable dryer (hi) to form anhydrous Zn'SO4 before its addition to. the "electrolytic circfuit. Either the ZDSO -6H2O or the anhydrous ZnSO4 are preferably added to the electrolytic circuit-by dissolving'in the electrolyte in suitable. agitators between separate divisions of cells-in the'lat er.-

of the circuit By the addition (J1me 'Zn SOf tothe solution in the electroly'iccircuitit-is pos- 'tion and highlcurrent density without depleting sible'toopera-te with every high acid concen'tra the zinc-in'the circuit below the limit necessary to'secure a high current .efiiciency.'. For'example,

' with a substantially saturated neutral the required anode and cathode surface in the electrolytic plant' to less half than that re- If it isidesi'red cuit with very concentrated ZnSOisolut'ion and -low'acld concentration. so as tobe able to use carrying 200 g. Zn per litre, lt'lS' posel m sible to precipltate all of this zinc by the-independentaddition of more ZnSO J as the zinc in solution is'deple'ted. It is thus possible .toIop- Jerate withacid concentration of 30% to .tor even slightly higher,- since. these solu'ions will from 114 to 110 g.-of'zinc per litre which is sufilcient to give an economical currente'fiiciency at veryhlgh-current densities. It is thus-possible by operating at these high current densities to'cut quiredin the circuitemling with the lower acid operate the electrolytic ai a very'..highcurrentfdensity with a high icurrent' 'emciency this may be done by the'moclificationi of the'p'rocess shown in Fight In thiscase'the fzinc sulphide ore or concentrate is treated in '1 the; sulphator- (1). with the .h'Ot 'Jacid' two-+% H2804) as previously-described. The excess of. hot-acid is separated in the filter- (2 andreturned 'to the head of the circuit .iorthe-treat- I ment-ofvmore ore, through the heater. (3) in which the =-acid consumed. intreating the 'ings from thistreatment maygo to a-brine'leaching or flotation treatment as previously described.v

eases the zinc is precipitated as Zn'S and the ore is also added as indicated. The ZriSOl is thenwashed out of the filter cakefrom '(2) with watersin a suitable washer (4). (preferably a counter current type) and filter (4a) The tail- The acid ZnSO; solution from the washer (4) is.

.no'w neutralized with oxidized zinc ore (or. zinc may be .flltered out of. the concentrated acid and dried'to form anhydrous ZnSOl by heating to drive ofi the H2804; The anhydrous ZnSO4 may then be dissolved in water andthe impurities may .be oxidized and'precipitated as" previously de-' scribed-to form the neutral ZnSO solution. The .neutral ZnSO4 solution is then treated with zinc dust in the precipitator (10) to precipitate the traces .of lead-and the copper and cadmium, which are removed from solution in the filter (10) The clean neutral ZnSO solution is now mixedwith a C8012 solution in .the precipitator (2.0)v preci'pitating the sulphion fromsolution as (lasoland ..torming"a'ZnCla solution as indicated in the following equation, 7

' znso +cac12=znc1=+caso4 (The CaSOr'is separated from the ZnCh solution in the filter (21). The. zinc is then precipitated from this zincchloride solution in the precipita-- tor- (22) by means of H25 for example that generated by treatment .of the zinc sulphide ore in thesulphator (l) and a suitablelime compound by one of the following methods; the solution may be treatedwith the H28 together with finely divided CaCOa' as described in my U. S. patent application 66,400,filed-Nov 2, 1925, (now Patent No.' :1,886,1'6 2) thusprecipitating the zinc as or the H18 may be absorbed .in'anen'iulsion of 'Ca(0H).z toform a; Ca(SH)z solution andthis- 211s and forming. each msolution'a's' indicated 12o '.solutlon-'may be 'used to precipitatev the zinc dir'ectlyas indicated inthefollowing equationi z'ncn+ca'.(sn 3=zns+cac1=+ms 5n preferably by mixing. the car-sun solution with-finely divided CaCOa in equimolecular pro portion to the CMSH) and using thismixture to precipitate the zlncas indicated below:..

v zzns zc-achq coauno and as described in my copending- 'U.. S; applicatlOh N0, 4 93,685,'filed ,NOV. 5, 1930 and in N0. 565,153, filedfSept; 25, 1931. In alljthese DIOG- chlorine remains inv solution as 021012. The- CaCl solution. formed is used to precipitate the- CaSO4 as described above and as. indicated in the flow sheet of Figl.6. The (33,804 filtered out in the filter (20) may be used for making high grade gypsum plaster or for other purposes. The precipitated zinc sulphide is filtered out of the CaCl -solution' in the filter (23) and treated with exit solution from. the electrolytic circuit (12), intheneutralizer (24) ,.the acid in the solulee silver thus be used over again for this purpose.

nes'aess tion being neutralized and the solution regenerated by the formation of 210804, and the HzS being driven off as indicated in the following equation:-

ZI1S+H2SO4=ZI1SO4+H2S A concentrated ZDSO4 solution (preferably hot) is used in closed circuit with the neutraiizer (22) and electrolytic cells.(12) and is rapidly vcirculated so as to prevent the acid generated by the electrolysis building up to any appreciable concentration. All the cells in the electrolytic circuitm'ay thus be operated continuously with a nearly neutral hot concentrated zinc sulphate solution, makingit possible to use very high current densities with a high current efiiciency. The H28 generated in the neutralizer may be returned to the sulphhydrate plant or maybe burned in a Claus kiln to recover the sulphur, or

may be utilized for other purposes. Traces of chlorine may be removed from the neutralized solution before its return to the electrolytic cells by the'addition of silver sulphate to the solution.

The silver chloride thus precipitated may be treated-to form silver sulphate again and the -If desired the ZnSfrom the filter (23) may be dried and heated to form a zinc sulphide paint I pigment as described in my U. S. patent applications Nos.- 493,685 and 565,153, instead of. going to the electrolytic plant.

1 As previously noted the-process is adapted to the treatment ofall classes of zinc sulphide ores and concentrates andtogether'with these for thetreatment of oxidized or carbonate ores. It is especially adapted, when used in connection with the brine leaching process of my U. S. Pat-f ents 1,539,711 and 1,539,712, for the treatment of bulk concentrates fromcomplex lead-zinc-iron sulphide ores, and forthe treatment of mixed" lead zinc carbonate ores. By thiscombination of, processes the zinc is first extracted from the I concentrates by the-process described above and for the 'a high grade iron product whichmaybe marketable. The $02 produced in'roasting the pyrite concentrate may be used for the production or 112804, liquid S0: or may bemixed with the HzS from the leaching operations to produce sulphur as indicated in the following equation:

v .21 12s+s0i=2Hio+3s By sucha combination oi'proces'ses used in connection with this invention, described herein, a

substantially complete recovery of all the metals in a complex lead-zinc-iron sulphide ore may be recovered in valuable marketable products.

Having described my process what I claim and desire to patent is:

1, The process of treating zinc sulphide ores, concentrates, and the like, which comprises grinding said initial material with hot relatively concentrated sulphuric acid in anamount which is only a small fraction of that amount which would be required to dissolve the zinc sulphate formed bysaid treatment, and thereby decomposing zinc sulphide in said initial material and forming zinc sulphate therefrom in solid form,

the brine-leached residue .in.

and thereafter separating excess acid out of its I mixture with said. solid zinc sulphate and ore residue, and returning said .acid for the treatment of more of the initial material as described, and dissolving said solid zinc sulphate and residual acid in water to form an acid zinc sulphate solution and separating said solution from said ore residue, and neutralizing. the acid in said solution, and treating the neutral zinc sulphate with an amount of calcium chloride sufllcient toreact with the zinc sulphate in said solution and form zinc chloride,

2. Process as 1n initial zinc sulphate solution, is treated with an oxidized zinc compound and'an oxidizing. agent' toneutralize and purify said solution, and then 1 claim 1, in which the acid is treated with metallic zinc to precipitate metals below zinc in the electromotive series.

3. Process as in claim 1, in which the acid initial zinc sulphate solution, is treated with an oxidized zinc compound and an oxidizing agent to neutralizeand purify said solution, and this is treated with metallic zinc to precipitate metals below zinc in the electromotive series'and thereafter calcium chloride is added to the-purified -zino sulphate solution, precipitating calcium sulphate, and treating the zinc chloride solution with H28 and a basic calcium compound to precipitate. ZnS. 4.-Process as in claim 1, in which the initial zinc sulphate solution is purified and then treated with calcium chloride, the precipitated C8504 removed and calcium sulphhydrate added to the -ZnC1z solution, to precipitate ZnS.

5. A process of treating zinc sulphide ores, concentrates and like material containing ZnS, which comprises grinding-said initial material with hot concentrated sulphuric acid, to convertthe ZnS into s01id'ZnSO4, the sulphuric acid being in substantial excess over the amount theoretically needed for that reaction, but being only a small the excess of concentrated sulphuric acid fromthe sulphated residue, dissolving the solid ZnSOa with residual acid adhering thereto, in water to .form an acid solution of zinc sulphate, and separating suchsolution from theore residue, treating suchacidsolution with an oxidized zinc compound and an oxidizing agent, to neutralize and purify the same, treating the solution with metalzinc to precipitate 'metalsbelow zinc-in the electromotive series of metals, and treating the so purified Z'nSOr solution with CaCh solution to 1115 fraction of the amount which would be needed to' dissolve all of the ZnSO4 formed, separating precipitate CaSO and to form a ZnCl: solution,

treating the latter-with a-sulphide' capable" oi precipitating ZnS, removing the latter and wash- .ing it free fromsoluble. chlorides, and adding.

said ZnS to theelectrolyte in an electrolytic circuit to form ZnSOi therein, and electrolyz ing the last mentioned liquor to recover metallic zinc therefrom.

. 6. A process of treating zinc sulphide ores, concentrates and like material containing ZnS, which comprises grinding said initial material with hot concentrated sulphuric acid, to convert the ZnS into solid ZnSO4, the sulphuric acid being in substantial excess over the amount theoretically' fraction of the amount which would be needed to dissolve all of the ZnSO4 tormed, separatingthe excess of concentrated sulphuric acid from needed for that reaction, but being only a small the sulphated residue, dissolving the solid ZnSO with residual acid adhering thereto, in an aqueous liquid to-form an acid solution of zinc sulphate, and separating such solution from the ore residue,

treating such-acid solution with an oxidized zinc ' compound and an oxidizing agent, to neutralize and purify the same, treating'the solution with metallic zinc to precipitate metals below zinc in the electromotive series of'metals, and treating the so purifiedZnS04 solution with calcium chloride solution to precipitate calcium sulphate and leave a solution of zinc chloride, and thereafterv treating said zinc chloride'solution with a sulphide 1 compound, to precipitate the zinc in the form of sulphide;

-7. A process of treating zincsulphide ores, conce'ntrates and like materials containing ZnS,

.which comprises grinding said initial material small fraction of the amountwhich would be. v

needed to dissolve all of the ZnS 04 formed, separating the excess of concentrated sulphuric acid from the sulphated residue-dissolving the solid ZnSO4 with residual acid adhering thereto, in an I aqueous liquid to form an acid solution of zinc sulphate, and separating such solution from the ore residue, treating such acid solution with an oxdized zinc.com pound and an oxidizing agent,

to neutralize and purify the same, treating the solution with metallic zinc to precipitate metals below zincin the electromotive series of metals, and treating theso purified. ZnSOisolution with calcium chloride solution toprecipitate calcium sulphate and leavea solution of zinc c'hloride,.

and thereafter treating said zinc chloride solution withcalcium sulphhydrate to precipitate the zinc in the vform of sulphide.

NIELS c. CHRISTENSEN. 

